1. Technical Field
The present disclosure relates to a wireless communication device and a wireless communication method.
2. Description of the Related Art
Heretofore, indoor communication has been the main target of the efforts of the wireless LAN standard in IEEE 802.11. Additional physical layer standards have followed, primarily with the aim of increasing transmission capacity, such as 802.11b (up to 11 Mbps), 802.11a/11g (up to 54 Mbps), 802.11n (up to 600 Mbps), and 802.11ac (up to 6.9 Gbps). Meanwhile, as the development of smart meters for realizing smart grids intensifies, demand is rising for low-rate, long-range outdoor transmission. Debate also continues over issues such as the allocation of usable frequencies for specified low-power wireless intended for such applications. Given this background, the formulation of a new communication standard using the sub-GHz band (the frequency band slightly lower than 1 GHz) is now being investigated. Additionally, in 2010, an IEEE 802.11 task group focused on developing a wireless LAN standard using the frequency band up to 1 GHz, TGah (802.11ah) was also formed. The specification framework for TGah (802.11ah) achieves a data rate of up to 100 kbps, and a maximum transmission range of 1 km.
In standards since IEEE 802.11a that use OFDM modulation schemes, including TGah (802.11ah), a preamble at the beginning of a packet is used to establish various synchronizations, and burst communication is conducted. The preamble is made up of a short training field (STF; also called the short preamble) and a long training field (LTF; also called the long preamble). The STF is used for automatic gain control (AGC), or automatic frequency control (AFC) to conduct rough adjustment. The LTF is used for AFC to conduct fine adjustment, or channel estimation. Also, after the preamble, there is placed SIGNAL information for controlling a data field (also designated “DATA”). The SIGNAL information is multiplexed by BPSK modulation that is strong against interference.
In TGah (802.11ah), it is anticipated that the standard will require a compatible communication device to be equipped with a function for communicating using the 1 MHz and 2 MHz signal bands. Consequently, in a communication network formed by communication devices conforming to 802.11ah, the formation of a communication network using both 1 MHz and 2 MHz as signal bands is anticipated. In other words, an environment of coexisting 1 MHz/2 MHz channels is anticipated.
Accordingly, when conducting communication based on 802.11ah, a communication device may need to determine whether a communication peer is transmitting using 1 MHz or 2 MHz as the signal band.
Similarly to 802.11ah, IEEE 802.11n is another standard that communicates by switching between multiple transmission modes within a communication network conforming to the same communication standard. Japanese Unexamined Patent Application Publication No. 2010-109401 discloses a method of efficiently determining the transmission mode (transmission format) in 802.11n.